The present invention relates to a process for producing 1,1,1-trifluoroacetone that is useful as an intermediate of pharmaceuticals and agricultural chemicals, or as a reagent for introducing fluorine-containing groups.
U.S. Pat. No. 6,262,312 B1, corresponding to Japanese Patent Unexamined Publication 2000-336057A, discloses a process for industrially producing 1,1,1-trifluoroacetone by reacting in a liquid phase 3-halogenated-1,1,1-trifluoroacetone (hereinafter xe2x80x9chalogenated trifluoroacetonexe2x80x9d), which is represented by the following general formula [2], with metallic zinc in a solvent of a proton donor. 
where X is a chlorine, bromine or iodine; and n is an integer of 1-3.
U.S. Pat. No. 6,340,776 B2, corresponding to Japanese Patent Application Serial No. 2000-309649, discloses a process for producing 1,1,1-trifluoroacetone by conducing in a gas phase a hydrogenolysis of the halogenated trifluoroacetone represented by the general formula [2], using a metallic catalyst.
It is an object of the present invention to provide a process for efficiently producing 1,1,1-trifluoroacetone using as a raw material a tetrafluoroacetone of the general formula [1] containing four fluorine atoms, 
where X is a chlorine, bromine or iodine, and n is an integer of 0-2.
Since carbon-fluorine bond is stronger than each of carbon-chlorine bond, carbon-bromine bond and carbon-iodine bond, it is more difficult to replace the fluorine atom of CH2xe2x88x92nXnF group of the tetrafluoroacetone with hydrogen, as compared with the halogen atom of CH3xe2x88x92nXn of the trifluoroacetone. If the reduction conditions are made too severe in order to increase the reactivity, the carbonyl group and the trifluoromethyl group are subjected to hydrogenation.
It is therefore a more specific object of the present invention to provide a process for producing 1,1,1-trifluoroacetone from the tetrafluoroacetone in a manner to efficiently convert CH2xe2x88x92nXnF group of the tetrafluoroacetone into methyl group and to substantially suppress the hydrogenation of the carbonyl group and the trifluoromethyl group of the tetrafluoroacetone.
According to the present invention, there is provided a process for producing 1,1,1-trifluoroacetone. This process comprises conducting in a gas phase a hydrogenolysis of the tetrafluoroacetone, which is represented by the general formula [1], by a hydrogen gas in the presence of a catalyst comprising a transition metal (e.g., ruthenium, palladium, platinum, iridium, rhodium, nickel, and a mixture of these).
According to the present invention, it is unexpectedly possible to efficiently achieve selective hydrogenation of CH2xe2x88x92nXnF group of the tetrafluoroacetone into methyl group and thereby to easily and efficiently obtain 1,1,1-trifluoroacetone with a remarkably high yield.